1. Field of the Invention
The present invention relates to an aircraft window and more particularly to an aircraft windshield with an outer glass ply spaced from an inner ply by a pressurized air gap.
2a. Technical Considerations
As an aircraft flies to higher altitudes, the air within the aircraft cabin is pressurized. As a result, the windows in the aircraft experience cyclic loading each time the aircraft internal pressure changes in response to the altitude. This cyclic loading on polycarbonate plies of the windows may lead to premature fatigue failure. In addition, the internal pressure causes the outboard polycarbonate or polycarbonate laminate ply of the aircraft window to deflect outwardly, changing its surface configuration. This effect is particularly important in military aircraft where a change in a surface configuration reduces the aircraft's ability to avoid radar detection. Furthermore, the outer polycarbonate surface is subject to abrasion and environmental degradation.
It would be useful to have an aircraft window, and in particular an aircraft windshield that avoids these deleterious effects while providing a structurally sound transparency capable of withstanding impacts that are typical in an aircraft windshield.
2b. Patents of Interest
Bayer U.S. Pat. No. 4,299,639 teaches a laminate assembly of two or more parallel glass panes and one or more layers of transparent synthetic plastic material plies. The glass panes are initially spaced apart by an airspace that is subsequently filled with the plastic material, which is injected into the air gap in a liquid state.
Medlin U.S. Pat. No. 4,333,282 teaches a multilayered bulletproof window including a multilayered outer section with an outer safety plate glass ply, and an inner section composed of polycarbon laminate. The inner and outer sections are separated by a space containing dry nitrogen gas at about 21/2 lbs per square. inch of pressure. The space is necessary to allow for differential rates of expansion and contraction of the sections and layers without damaging the window.
Litchfield et al. U.S. Pat. No. 4,525,966, teaches a window system construction including spaced apart glass panes within a window frame. The window construction includes glazing beads inserted between the glass plies and the frame which incorporates an arrangement to prevent disengagement of the glazing beads other than by breaking the glass plies.